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Your search keyword '"Kontogeorgis, Georgios M."' showing total 970 results
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970 results on '"Kontogeorgis, Georgios M."'

3. Unraveling thermodynamic anomalies of water: A molecular simulation approach to probe the two-state theory with atomistic and coarse-grained water models.

Author

Muthachikavil, Aswin V., Sun, Gang, Peng, Baoliang, Tanaka, Hajime, Kontogeorgis, Georgios M., and Liang, Xiaodong

Subjects
MOLECULAR dynamics
Abstract

Thermodynamic and dynamic anomalies of water play a crucial role in supporting life on our planet. The two-state theory attributes these anomalies to a dynamic equilibrium between locally favored tetrahedral structures (LFTSs) and disordered normal liquid structures. This theory provides a straightforward, phenomenological explanation for water's unique thermodynamic and dynamic characteristics. To validate this two-state feature, it is critical to unequivocally identify these structural motifs in a dynamically fluctuating disordered liquid. In this study, we employ a recently introduced structural parameter (θavg) that characterizes the local angular order within the first coordination shell to identify these LFTSs through molecular dynamics simulations. We employ both realistic water models with a liquid–liquid critical point (LLCP) and a coarse-grained water model without an LLCP to study water's anomalies in low-pressure regions below 2 kbar. The two-state theory consistently describes water's thermodynamic anomalies in these models, both with and without an LLCP. This suggests that the anomalies predominantly result from the two-state features rather than criticality, particularly within experimentally accessible temperature–pressure regions. [ABSTRACT FROM AUTHOR]

Published
2024
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10. Prediction of water anomalous properties by introducing the two-state theory in SAFT.

Author

Novak, Nefeli, Liang, Xiaodong, and Kontogeorgis, Georgios M.

Subjects
POLYWATER, SPEED of sound, CHEMICAL equilibrium, EQUATIONS of state, LOW temperatures
Abstract

Water is one of the most abundant substances on earth, but it is still not entirely understood. It shows unusual behavior, and its properties present characteristic extrema unlike any other fluid. This unusual behavior has been linked to the two-state theory of water, which proposes that water forms different clusters, one with a high density and one with a low density, which may even form two distinct phases at low temperatures. Models incorporating the two-state theory manage to capture the unusual extrema of water, unlike traditional equations of state, which fail. In this work, we have derived the framework to incorporate the two-state theory of water into the Statistical-Associating-Fluid-Theory (SAFT). More specifically, we have assumed that water is an ideal solution of high density water molecules and low density water molecules that are in chemical equilibrium. Using this assumption, we have generalized the association term SAFT to allow for the simultaneous existence of the two water types, which have the same physical parameters but different association properties. We have incorporated the newly derived association term in the context of the Perturbed Chain-SAFT (PC-SAFT). The new model is referred to as PC-SAFT-Two-State (PC-SAFT-TS). Using PC-SAFT-TS, we have succeeded in predicting the characteristic extrema of water, such as its density and speed of sound maximum, etc., without loss of accuracy compared to the original PC-SAFT. This new framework is readily extended to mixtures, and PC-SAFT-TS manages to capture the solubility minimum of hydrocarbons in water in a straightforward manner. [ABSTRACT FROM AUTHOR]

Published
2024
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11. Ion–ion association is lost by linearizing the Poisson–Boltzmann equation when deriving the Debye–Hückel equation.

Author

Silva, Gabriel M., Liang, Xiaodong, and Kontogeorgis, Georgios M.

Subjects
HELMHOLTZ equation, HELMHOLTZ free energy, ION-ion collisions, BINDING constant, ACTIVITY coefficients, ELECTROSTATIC interaction
Abstract

In this work, we demonstrate how the ion association constant can be attributed to the difference between the full Poisson–Boltzmann equation and its linearized version in very dilute solutions. We follow a pragmatic approach first by deriving an analytical approximated solution to the Poisson–Boltzmann equation, then calculating its respective Helmholtz free energy and activity coefficient, and then finally comparing it to the contribution from the mass action law principle. The final result is the Ebeling association constant. We conclude that electrostatic ion–ion interaction models miss the ion association contribution naturally introduced in higher-order electrostatic theories. We also demonstrate how the negative deviations from the Debye–Hückel limiting law can be physically attributed to the ion association phenomenon. [ABSTRACT FROM AUTHOR]

Published
2024
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